Composition of matter for platinum substitute.



F. A. FAIIRENWALD.

COMPOSITION 0F MATTER FOR PLATINUM SUBSTITUTE.

APPLICATION FILED IuLv I3, 191e.

l ,296,938. Patented Mar. 11, 1.919.

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UNITED STATES PATENT oEEIoE.

FRANK A. FAHRENWALD, 0F CLEVELAND, OHIO, ASSIGNOR TO THE RHOTANIUMCOMPANY, 0F CLEVELAND, OHIO, A. CORPORATION OF OHIO. v

COMPOSITION OF MATTER FOR PLATINUM SUBSTITUTE.

specification of Letters Patent. Patented Mar, 11, 1919 Application meaJuly 13.1916. serial No. 108.991.

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Be it known that I, FRANK A. FAHREN- WAL, a/citizen of the UnitedStates, residing at Cleveland, in the county of Cuyahoga and State ofOhio, have invented a certain new and useful Improvement in Compositionsof Matter for Platinum Substitute, of which the following is a full,clear, and exact description, reference being had to the accmpanyingdrawings. in a loys, and has for its object to provide a com osition ofmetal which may be employe in many cases asa metallic substitute forplatinum and expensive platinum alloys in various typesI of electricalconstruction, spark devices, resistance elements, thermo-coupleelements, etc.) and in articles of jewelry, chemical containers, and thelike, thus effectively conserving this scarce and valuable metal forthose scientific purposes in Iwhich its use is at present imperative.

The physical and chemical properties that I have developed in my alloyare the result of scientific investigations covering a period of years,and they selection of the components of my alloy, and the adjustment ofthe proportions of these components, are based upon a study of therelations of each metal to the other, and to the alloy body as a whole.

In view of thisfact, I consider it advisable to describe in some detailthe methods and principles that I have discovered and used in workingout my invention. Before undertaking the development of a new materialthat would serve instead of platinum in its various applications, it wasnecessary to adopt certain criteria which should serve as specificationsfor physical and chemical properties of any material that would besatisfactory.

- high temperatures are the prime requisites,

invention relates to an improvement y These requirements inV a platinumsubstl'tute may be detailed as follows:

1. Its melting point should be higher than pure gold. (This would not benecessary in artlcles of jewelry and the like but for general chemicalware and units of electrical construction high melting-point isimperative.)

2. It must not be affected by chemicals or gases encountered in itsapplication.

3. It must not oxidize at any temperature up to and including thatnecessary to melt it. (This is very necessary in chemical applicationsand of great importance in the case of spark devices. I have observedthat the arcing produced in many Vbreaker designs is sufficient to meltthe surface of even pure platinum. A` careful microscopical examinationof the surface' of a used point Y duced on the contact surface of thepoints themselves by this conditionA of local high temperature, thecircuit would be broken, or at least it would be most diilicult to startthe device after it had once been stopped, duev to thel insulatingeffect of .this oXid film. This is the chief objection to the use oftungsten contacts.) i

4. It must possess sufiicient strength and hardness to withstandstresses tending to change its form while in place. (Even pure platinumis deficient in this property, but this is'often overcome by adding upto30% of iridium, which, however, greatly increases the cost. In myexperiments with contact devices it was observed that soft metals suchAas gold, were battered out of shape by the continued hammering'efect.Strength is very valuable in chemical and other electrical constructionalso.) y

5. The electrical resistance should preferably be greaterthan that forplatinum. (A material of this nature often finds applica- `tion inelectrical heating units. I have found that low electrical conductivityis not amount of current carried is very small for the large crosssection employed, while the thermal and electrical resistance acrosssurfaces of contact formed in fastening are very greaJ vhen comparedwith that of the metal itsel 6. It must Abe suliciently malleable andductile to permit of rolling, drawing, stampin or otherwise working, toa desired shape.

g. Its cost of production must be low as compared with that of platinum.

It will be seen at once that the above requirements of physical andchemical stability at high temperatures form a set of specifications ofa very exacting nature, and at once exclude from consideration allmetals of a readily fusible or oxidizable nature.

A consideration of all materials at present available, using the abovespecifications as criteria, proved that no single metal was suitable.,It was evident, therefore, that any Search forv the rdesired materialmust be in the field 'bf alloys, since experience has shown that thephysical and chemical prop erties of a metal may be radically changed bythe addition of varying amounts of another elem'ent, or of severalelements.

Vhen two or more metals are brought together in the liquid state, theybehave exactly like two ordinary liquids. When the temperature islowered the solidified mass may contain any one of the fourfollowing-constituents: pure components; solid solutions; compounds; andeutectics-or some combination of these. While a theoreticalcontemplation of the properties of diil'erent metals will to some extentsuggest the probable properties of an alloy thereof, still it is only byexperiment and .test that its mechanical and physical properties can beabsolutely settled. However, if a certain application is desired as inthe problem under consideration, a definite limit may be placed upon thenumber and amount of constituents permissible.

Fortunately, the number of fundamentaly conditions is limited to four,as given above. Pure metals impart their own characteristics; solidsolutions are, in general, of a ductile and malleable nature (if formedof ductile metals, or of a preponderance of one ductlle metal) compoundsand usually, eutectlcs, are hard and brittle; while the latter, evenwhen plresent in very small amounts, tend to soli ify between the grainsof the alloy, thus producing segregation and destroying its ductility.

Alloys of the solid-solution type would therefore produce the mostsatisfactory platinum substitute, for compounds are too brittle topermit of being worked, while the segregation produced by eutecticswould produce selective erosion and corrosion. The alloying of metalsserves to increase hardness, to produce resista/RCC t0 QOI'IOSOLI,

etc., but my experiments have shown it will not prevent oxidation at ornear the melting temperature. For instance more than a trace of basemetal, as copper, nickel, iron,

etc., in any of the precious metals will cause present in appreciablequantities, wherefore the substance sought must be a solid solutionalloy of two or more of the noble metals silver, gold, palladium,platinum, rhodium, iridiu'm, ruthenium and osmium.`

In view of the fact that a substitute for platinum was the object of myresearches, this metal was not to be included to more than very smallamounts, in the desired alloy. Likewise the metals rhodium, ruthenium,osmium, and iridium are too rare and costly to be used at least in largeamounts, in an inexpensive platinum substitute.

Thus after my researches had included the entire list of elementsseparately, it` was found that only gold, silver, and palladiumfulfilled to the greatest degree, the preliminary set of governingspecications. Not one of these, however, was suitable, when used alone.Silver is too soft and of too low melting point, and is not suliicientlychemically inert. Gold, also, is not sufliciently hard or refractory,while palladium alone is too costly.

These three metals form solid solution binary and ternary alloys in allproportions, although it is found that differences in composition"V havevery great eil'ects upon the hardness, meltin chemical resistivity ofthe resulting alloy. Some of these effects are illustrated graphicallyin the drawing accompanyin and forming a part of this application wereinFigure 1 represents the hardness curve and melting point curve forgold-silver alloys; 7Fig. 2 the similar curves for the silver palladiumalloys; Fig. 3 the similar curves for the gold palladium alloys; Fig. 4represents a photomicrograph section of the gold palladium alloy, Fig. 5a photomicrograph section ofthe sllver palladium alloy; Fig.

pomt and electrical and 6 a diagram showing the melting points of.

other increases the hardness to a remarkable extent. This is shown inthe curves given for the three binary series .of old-silver,silver-palladium, and gold-pa.l adium, fFigs. 1, 2 and 3, respectively.These metallic solid solutions are truly crystalline, and in thecrystalline arrangement (or space lattice `The space volumes occupied byatoms of different elements are not the same, so that, if the metals,whose atomic volumes are not equal and whichl possess other intrinsicdifferences, form symmetrical, solid-solution-space lattices, there mustresult a contraction of the larger atom and-an expansion of the smaller,and other energy adjustments,thus producing an internal strain whichincreases the hardness, lowers the electrical and thermal conductivity,and variously affects other properties of the components.

It is evident also that this internal strain and the corresponding.resulting properties will be a function of the number of atomsdissolved. This is shown in the case of the hardness curve, which showsa maximum at the point where equal atomic proportions prevail, z. e., at50 atomic per cent. of each component in a binary series. The curves forelectrical and thermal conductivity likewise show a minimum at thiscomposition. Experiment proves that those metals, like gold and silver,which possess the most nearly equal atomic volumes will replace eachother and form solid solutions most readily and with the least amountofsegregation.V Their atomic volumes are: gold, 10.20; silver, 10.23.Palladium, however, with an atomic volume of 8.9 tends to segregate uponsolidiication of thebinary allo with either, as shown in Figs. 4 and 5 wich are photo-micrographs, showing the.

internal structure of silver-palladium -and gold-palladium alloysrespectively, this tendency being partiularly marked in the case ofpalladium silver alloys. I-have discovered, however, that the additionof a quantity of gold to this palladium-silver alloy markedly decreasesthe segregating tendency arid signally improves the character of thealloy in other respects. Y"

I have, therefore, discovered that a ternary alloy containing gold,silver, and palladium fulils the requirements of a platinum substitutein a remarkable degree. The pro-y portions ofvthese ingredientsmay bevaried through a considerable range depending upon the price limitationsand the rigidity of the requirements.l The addition of silver to analloy of gold and palladium even up to 50 atomic per cent. hascomparatively small effect upon the melting point of the composition butdecreases the cost per unit volume in great degree, and in case ofalloys containing a relatively low per cent. of palladium is of materialservice in increasing the hardness.

The addition of palladium even in small quantities to alloys of gold andsilver greatly increases the melting point and hardness and chemicalresistivity. The addition of gold to alloys of silver and palladiummarkedlydecreases the segregating tendency and increases its chemicalresistivity.

The portion of Fig. 6 included withinthe heavy line thereon indicatesthe area of most valuable commercial percentages, those alloyscorresponding to the lower right hand portions of this area being theleast expensive though ysuiciently conformin to the above expressedbasic requirements or many electrical purposes. Alloys corresponding toportions above and toward the left will conform to more rigidrequirements. For example any alloy fallin within the left hand half ofthis area exhi its the most perfect physical 'and chemical stability athigh temperatures, fully comparable in most of its applications to thatof platinum. n Investigation of these ternary proves the following: (l)That the addition of over one per cent. of silver to any alloycontaining gold and palladium increases the hardness up to a certainlimit, lowers the melting point very little, and at the same timedecreases the cost.

The increased hardness is. very valuable, in many cases where increasedsilver is not objectionable and the decreased cost is of importance. Byadding varying amounts of silver therefore, I obtain the same necessaryhardness as would be obtained by using higher percentages of palladium,as shown on Fig. 3. For certain chemicalapplications `of rigidrequirements, however, I use the pure binary alloy of gold andpalladium.

(2) -The addition of more than 10 atomic of palladium to the gold-silverseries raises the melting point to a degree where ltheV alloys canwithstand high temperatures without fusing. The approximate meltingpoint of any alloy within the diagram may be judged from its positionwith reference to the series of dotted lines which areJ drawn throughpoints representing alloys of equal melting point. These lines aremarked 11000' C.,l150 C.,1200 C.,etc. The alloys decrease in degreeofnobility from thegold end of the series, but to a very slight extentfor small amounts of silver but the increased hardness. increasedelectrical resistance and decreased cost in many cases more than balancethis.

3) The addition of more than 5 atomic of gold to the silver-palladiumalloys reduces segregation, reduces volatilization and alloys increasesresistance to erosion and corros1on.

(4) I ernary'alloys of these vthreemetals` are more satisfactor than asilver-palladlum or gold-silver blnary alloy of any com;

position.

Limits ofA palladium.

4 Because of the results of my experiments as outlined above, and theirevident lrelation to theatomic proportions of these elements,

y I have based my descriptions and claims upon the relative number ofatoms or atomic percentages of each element present.. My experimentshave shown that a melting point of at least 1150o C. is necessary in aplatinum substitute to be used under most avorable conditions.

lixed the lower limit for palladium content I, therefore, have to alinecoinciding with that dotted line representing a melting temperature of1150 Because of high cost andl other undesirable features, as tendencyto segregate, etc., I ix the upper limit of palladium at 40 atomicLimits of gold.

I have found'that at least 5 atomic of gold is required Ato producehomogeneous la1- loys, and to reduce excessive spark erosion and 80atomic of that element.

Alili Lim/its of silver.

My experiments have shown that, for certain purposes where increasedhardness or electrical resistivity is required, itis advisable to addover 1 Iatomic of silver. I have found that rhodium, iridium, etc., arebetter than silver but too costly;

If conditions of application are not too r1g1d, even up to 75 atomic ofsilver may be used. The limits of total variation in composition aretherefore contained within the area bounded by the lines AB-BC-CD-DE-EF-FA.

By the term palladium asused herein I mean the commercial material whichcontains on the average about one-half of one` per cent. of platinum asan impurity and frequently other noble metals as gold, iridium, orrhodium; it is very? rarely free Afrom these substances, especiallyplatinum,

and in exceptional instances has run as high as ve per cent. of thatsubstance. I have always ignored this lnoble metal impurityas notinjuring the product, which from the nature of the commercial substancesused 'will frequently contain small percentages of these substances, inaddition to which small amounts of the same may be added as heretoforesuggested.

The alloys near the gold end of this area are more noble in character,are more insoluble in acids, and less afected by gases than those higherin silver. None, however, are in the least oxidized at any temperatureby arcing across terminals composed of them.

Below 5 atomic of silver these alloys are practically insoluble inboiling concentrated acids, as hydrochloric, nitric or in alkalis. Above5 atomic 'of become slightly soluble in nitric or sulfuric acids, thoughpractically insoluble in aqua regia.

It is advisable, but not necessary, to cool highpalladium alloys veryslowly to allow diffusion to take-place.

Having thus described my invention, what I claim is l 1. A platinumsubstitute containing palladium together with silver and one at least ofthe other noble metals immediately surrounding palladium in the periodictable, all of the 'constituent metals having atomic weights, between onehundred and two hundred times that .of hydrogen, the palladiumconstituting not less than ten atomic per cent. of the whole.

2. A platinum substitute containing palladium alloyed with silver andone or more of the metals in the gold series of the periodic table,I allthe constituent metals having atomic weights between one hundred an twohundred -times that of hydrogen, silver being preponderant, and thepalladium constituting not less than about ten atomic per cent. of thewhole.

3. A composition of matter for platinum substitute in electrical andchemical apparatus containing between ten and forty atomic per cent. ofpalladium, the remainder being gold and silver.

,4. A composition of matter containing palladium from 10 at. to `40 at.gold 5 at. to 80` at. and silver 1 at. to

5. A-compositionfof matter containing at least '10 atomic per cent. andnot over 40 atomic per cent. of palladium, at least 10 atomic per cent,and not over eighty atomic per cent'. of silver, the remainder being ametal or metals of the gold series in the periodic table having anatomic weight between one hundred and two hundred times that ofhydrogen. y

6. An alloy for the distributionof electric current by contact composedof gold and silver in approximately equal proportions and approximatelyten per cent. of,- palladium.

7 A11 alloy for the distribution of electricsilver, they 1,2ee,sas

current by contact composed of gold and silver with the addition of ten`per cent. of palladium.

8. An electric sparking terminal made 0f gold and silver in apreponderating degree with the addition of at least ten per cent. ofpalladium.

9. A11 electric current communicating element formed of an alloyconsistingy of approximately forty-five per cent. of gold, forty-*fiveer cent. of silver, and ten 'per cent. of pa ladium.

1,0. An electrlc current communicating element formed of an alloycontaining palladium and silver together with one or more of the othernoble metals immediately sur? rounding palladium in the periodictablekall of the constituent metals having atomic weights between onehundred and two hun dred times that of hydrogen and the palladiumconsti-tutin not less. than about ten atomic per cent. o the whole.

In testimony whereof, hereunto aix my signature,

FRANK A. FAHRENWALD;

